Depositing material on a substratum, defined by a piece to be repaired, by means of a technique called “electro-spark deposition”, also indicated as “ESD”, similar to micro-welding, is known and consists in transferring small drops of a molten material onto said substratum, starting with a consumable rotating electrode.
The material is transferred thanks to formation of electric sparks between the rotating electrode and the substratum. The electrode is simultaneously enveloped by a flow of inert gas which locally protects said electrode, the working area and the substratum. The drops of material are welded onto the surface of the substratum and form superimposed layers of coating material by repeatedly passing the rotating electrode over the substratum. At the same time, the combined action of rotation of the electrode and the pulse-type sparks prevents the electrode from welding to the substratum.
The electric sparks have a relatively high frequency but extremely short duration (a few milliseconds), so the material is deposited with a low thermal contribution and without causing overheating or thermally altered zones in the substratum.
However, the deposited material is uneven, due to its nature, since it is formed of small drops deposited onto each other. The rotating electrode effectively tends to touch the zones with peaks of material already deposited and to deposit other drops in these zones, accentuating the difference between peaks and valleys.
In order to overcome this problem, it is necessary to reduce the asperities of the surface which are progressively being formed, periodically interrupting deposition and compacting the layer of material deposited so far, before proceeding with deposition of another layer. In general, the surface asperities are lowered by means of hammering. This is an effective operation, but the quality obtained is not reproducible from one piece to another and sometimes, on a given piece, it is uneven for the entire extension of the material deposited.
Furthermore, hammering is not always controllable, so, on material with low ductility, hammering may cause micro-fractures which compromise functioning and/or duration of the repair.
Furthermore, hammering on pieces with a thin wall could cause deformations, which can only be partly limited through use of containment tools (such as an anvil).
As an alternative to hammering, compacting is performed by means of ultrasound technology, but this requires relatively expensive instruments.